Page:Popular Science Monthly Volume 15.djvu/37

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27
CLEWS IN NATURAL HISTORY.

cause the foot of the Hipparion to sink less deep into swampy soil, and be more easily withdrawn than the more simplified horse's foot." Furthermore, the ulna or bone of the forearm, deficient in the horse of to-day, is tolerably well developed in Hipparion.

Backward in time, and in the older Miocene formations of Europe, another fossil horse was disentombed, and was duly described under the name of Anchitherium. This latter horse possesses a completely developed ulna in the forearm, and fibula in the leg; but its chief point of interest lies in the fact that each foot possessed three fully developed toes (Fig. 12, DD1 d, d, c) which apparently must have touched the

PSM V15 D037 Evolutionary bone changes in horses.jpg
Fig. 12.

ground in walking. Already, our splint-bones are seen to better their condition as we pass backward through the ages, and to appear as the natural supports of well-developed second and fourth toes. Here the geological history of the horse in the Old World may be said practically to end. Modern history assures us that the first horses which peopled the New World, and whose descendants roam over American prairies as the famed mustangs, were imported by the Spaniards at the period of the Mexican conquest. Geology has a more curious tale to relate of the New World horses and their history, and gives them an antiquity compared with which the events of man's primitive history in either world are but as yesterday. Recent researches among the rock formations of Western America, in particular, have shown us that it is to the New World we must look for a perfect pedigree of the horse. For, beginning with the horse of to-day, with its splint-bones, we are carried gradually backward in time to the Pliocene horse of the New World named Pliohippus (BB1) — a form not differing materially from the living horse, but serving in a very graduated fashion to introduce us to the older Protohippus, the New World representative of our own fossil Hipparion (CC1), and in some respects a more typical three-toed